352 BELL SYSTEM TECHNICAL JOURNAL 



theorists wanders about in the most disconcerting way, so that often in a 

 single article the wording in one place will be intelligible only to a few 

 hundred (if so many) of the most advanced of specialists, and in another 

 will sound like the voice of Newton speaking out of the Opticks, only in a 

 much more cumbrous manner. 



In the atomic world we have already seen how gravitation is neglected, 

 being pushed into the background by the electromagnetic forces and the 

 cohesions and repulsions derivable from these. Now in their turn the 

 electromagnetic forces must recede into the background. This sounds 

 extraordinary. Have we not all been told of the supreme importance of 

 nuclear charges? Have we not been taught that by its charge a nucleus 

 attracts electrons and organizes them into a family about itself and so 

 creates an atom, — an atom which coheres with others, so that the world 

 as we know it is organized by the charges of nuclei? All this is true, and 

 very important from our viewpoint — but not so important, it seems, from 

 the viewpoint of a nucleus. To this little cluster of protons and neutrons, 

 the mass is more important than the charge; the total number of its com- 

 ponent particles is more important than the number of protons separately 

 or the number of neutrons separately; the cohesive forces are more impor- 

 tant than the electrical. Perhaps a nucleus cares little about its charge, 

 and nothing at all about the swarm of electrons which that charge coerces 

 to swirl about it like a cloud of flies, though if it were not for those swirls 

 the world would be barren and dead. 



The cohesive forces certainly overpower the electrical. We are in no 

 doubt of this, for the electrical forces are repulsive. Newton had gravity 

 available for binding his atoms together; it was of the right type but inade- 

 quate, so he gave it cohesion as an ally. The electrostatic force between 

 proton and proton is a repulsion, so to bind such particles together the 

 Newtons of nuclear physics must overcome it with cohesion as an adversary. 

 How greatly it is overcome is shown in much the same sort of way, as I 

 followed when invoking the vaporization of solids to show how greatly 

 the cohesion of atom with atom surpasses gravity. It is possible (at the 

 end I will mention how) to compare the amount of energy required for 

 tearing apart a cluster of two protons and a neutron with that required for 

 tearing apart a cluster of two neutrons and one proton. The two amounts 

 differ by only a few per cent; and more surprising yet, the former is the 

 greater! Though the first-named of the clusters contains the inherent 

 explosive power of two protons trying to drive themselves apart by the 

 long-range repulsion, it is stuck tighter together than the other, which 

 contains nothing of the sort. As a minor detail this shows that the cohesive 

 forces depend to some extent on whether the particles are neutrons or pro- 

 tons; but the major conclusion is, that the cohesive forces are the masters. 



